The basic technique of formation fracturing involves the injection of a fracturing fluid down the well bore to create and perpetuate fractures in the underground formation. The fracturing fluid is under high pressure, and must be able to survive the shear forces caused when flow is forced through casing perforations, other restrictions, and at the leading edge of the fracture.
Hydrocarbon gels are commonly used as fracturing fluids especially in cases where the formation is extremely water sensitive. The fluid viscosity is increased using phosphate esters such as mixed ethyl, octyl and decyl mono-, di- and triesters combined with metals, specifically ferric ions and aluminum ions. The metals are referred to as crosslinking agents.
Ferric salts used in the gelling of a hydrocarbon system for formation fracturing are described in U.S. Pat. No. 5,571,315, the contents of which are incorporated herein by reference. The use of amines and polycarboxylic acids to assist the gelling process are described in U.S. Pat. No. 5,647,900, the contents of which are incorporated herein by reference. Enhancers for use in the gelling of hydrocarbon liquids are known and described in U.S. Pat. Nos. 6,297,201 and 6,387,137, the contents of which are incorporated herein by reference.
Most formation fracturing involves onsite mixing of the fluid with short residence time in the surface mixing equipment. As a result, it is advantageous for gel formation to occur quickly upon mixing of the gelling agent and the crosslinker. Commercially available aluminum and iron solutions will form gels with phosphate esters in hydrocarbon liquids. It would be advantageous if such viscosity gain occurred quickly, allowing faster “mix on the fly” applications.
In addition, hydrocarbon gels are temperature sensitive, and the upper limit of stability can be under 100° C. There are many situations where enhanced temperature stability would be desirable.